This invention relates generally to the field of vertical Venetian blinds, and more particularly to an improved means for simultaneously rotating the vane elements thereof about the principal axes of the vanes when they are in relatively extended position at spaced substantially equal intervals along a supporting header element.
The use of a manually engageable elongated wand supported at an upper end thereof by the header element is well known in the horizontal type Venetian blind art, where the construction involves the use of a universal joint or equivalent means to transmit rotational movement imparted to the wand about a vertical axis to one about a horizontal axis. Because the horizontal type blind employs cords which pass over pulleys, the tendency of the cords to slip under excessive tension provides a built-in safety factor preventing damage to the blind components under misuse.
The provision of equivalent structure in a vertical type blind is somewhat more involved, since ball or bead chains, in order to transmit motion from a shaft, must entrain pulleys which are provided with indentations or recesses which correspond in size and spacing to the diameter of the individual balls or beads comprising the chain. Once engaged with such a pulley, slipping does not readily occur, and when excessive rotation of the wand occurs, damage to delicate parts of the blind normally results.
The provision of a friction clutch means in the motion train is an expedient readily occurring to a worker skilled in the art, but existing clutch structure known in other arts is relatively expensive to manufacture, and cannot readily be incorporated into a vertical blind header. The desirability of wand type adjustment means is well established by the convenience obtained in use, and that fact that the relatively rigid wand, when released by the user automatically returns out of the way beneath the header, so that it does not detract from the decorative appearance of the blind.